R12 WHEELER. [Vot. III. 
figured. Its chromatin is limited to a few filaments; whereas 
in Fig. 19 2 pz we have a long and intricately wound coil. 
The cleavage nucleus continues the course begun by the 
female pronucleus. Figure 21 represents it when it has reached 
the middle of the dorsoventral axis. The cytoplasm surround- 
ing this nucleus, which is drawn from an egg hardened in 
picrosulphuric acid, shows an astral radiation. The cytoplasm 
passes by insensible degrees into the surrounding homogeneous 
yolk substance. It is as if the female pronucleus when it left 
the polar globules took a little mass of the protoplasm abun- 
dant at that part of the egg’s surface and travelled with it, 
making it convert the yolk into protoplasm during the journey. 
As soon as the cleavage nucleus reaches the front edge of 
the mass of homogeneous yolk, or has advanced a very short 
distance further into the granular yolk, it stops and begins 
to increase in size till it becomes a clear vesicle (Fig. 22) in 
which the chromatin, broken into irregular fragments, lies scat- 
tered through the finely granular contents. The nuclear wall 
grows fainter and disappears. The large spindle now appears, 
and the typical process of karyokinesis is carried on (Fig. 
23). The polar axis of the spindle was in all but one of the 
many cases in which I observed the division, parallel to the long 
axis of the egg. In the exceptional case (possibly an abnormal 
egg) it was parallel to the dorsoventral diameter. Even before 
the division of the nucleus commences, the polar axis of the 
future spindle is foreshadowed, as it were, in the shape of the 
granular (amceboid) cytoplasm, which, as may be seen in Fig. 
23 cf, is elongated in a direction parallel to the cephalocaudal 
axis of the egg. The karyokinetic process employed in this 
and the subsequent divisions is typical. Soon after the nuclear 
wall again makes it appearance the two nuclei with the cytoplasm 
which surrounds them separate about one-fifth the longitudinal 
diameter of the egg, and then prepare for the next division. 
The polar axes of the two daughter spindles now formed are very 
nearly at right angles to the polar axis of the mother nucleus. 
In all the first divisions the perfect isochronism of the differ- 
ent stages in the different nuclei is striking. Fig. 24 represents 
two spindles from an egg containing four nuclei in exactly the 
same (metakinetic) stage. In this figure, taken from a longitu- 
dinal section, one of the spindles (c) has its axis at right angles 
